1. Field of the Invention
This invention generally relates to an improved dewatering machine and, more particularly, to an integral machine for the filtration and expression of liquids from solids.
2. State of the Art
Various machines are known to mechanically dewater liquid-solid mixtures such as sewage and waste sludges in large-scale applications such as municipal wastewater treatment operations. One commonly used machine is a rotary drum vacuum filter which utilizes suction to draw liquid from a slurry through a porous filter medium. As conventionally operated, that type of machine produces solid cakes that are fairly moist because the applied pressure differential cannot exceed atmospheric pressure and the moisture content of some solids cannot be reduced below certain values at such pressure differentials even at the expense of prolonged treatment times. Centrifuges are also frequently used in municipal waste treatment operations but are not entirely satisfactory for dewatering sludges whose specific gravity approximates that of water itself. Filter presses and other types of expression devices are also sometimes used for sludge dewatering but they have capacity limitations, especially for very watery sludges.
There is, however, a recognized need to provide sludge cakes which are substantially dryer than those which are conventionally produced. For instance, where sewage sludge is disposed of by means of incineration, increased cake dryness will reduce or obviate auxiliary fuel requirements to sustain combustion.